1. Field of the Invention
The invention relates to processes for recovering valuable organic compounds and materials from citrus fruit peel and in particular to the separation of valuable compounds and conversion of the peel to a flour useful for example in the baking industry.
2. Brief Description of Related Art
One of the major problems encountered over the years with respect to the production of citrus juice, citrus concentrate and sections has been the disposal of the various waste products including the peel, seeds, rag and pulp. For many years these materials were believed to be of little practical value and, accordingly, were simply disposed of as waste without being processed in any way.
In recent years, however, it has been found that certain of these waste materials (e.g., the peel) could be further processed to provide an excellent and highly nutritious cattle feed. Unfortunately, while the use of such processed wastes did help to alleviate a portion of the waste disposal problem, the processing of the wastes to provide cattle feed was not as economically attractive as had been hoped.
Accordingly, efforts have recently been made to process such waste materials to provide products which are suitable for human as well as animal consumption. It is also desirable to provide a diverse range of products from the processing of such materials in order to take full advantage of the raw materials contained therein. For example, the peel is a virtual chemical compound warehouse, containing many organic compounds useful as pharmaceuticals, fragrances, enzymes, food chemicals and the like. These chemical compounds continue to be wasted and not fully utilized.
Unfortunately, the waste materials are not easily processed. For example, U.S. Pat. No. 2,215,944 discloses a process where the orange peel is treated with lime to provide a product suitable for use as cattle feed. However, the use of lime is not advantageous as it generally yields a bitter tasting product.
In addition, the pectin which is present in the peel is destroyed or damaged during processing with lime, thus removing one of the desirable components in the peel from the standpoint of human and animal consumption. However, the peel is difficult to process without the use of lime or related materials (e.g., magnesium or aluminum containing compounds) since it is very slimy. The processed peel is also difficult to dry due to the cellular structure of the peel which is usually rendered less intact through contact with materials such as lime.
In addition, the peel contains a substantial amount of various sugars which are desirably removed from the peel in order to reduce the caloric content of the finished product. The sugars are very hygroscopic and, if present in significant amounts, also render the processed peel very difficult to dry. The peel also contains significant amounts of essential oils (i.e., naturally occurring volatile oils) which are the odor and/or flavor component of the peel. The essential oils can provide bitter or unpleasant taste sensations and are thus desirably removed from the peel.
As an alternative to lime processing, waste peels have been washed with water to remove portions of the sugars and bad flavors present. Such aqueous washing does not, however, remove much of the essential oils which are present. Carotenoid pigments also remain in the product, and after a short period of time, oxidize to produce an unpleasant "haylike" flavor. The water-washed products are also difficult to press in order to remove excess water. The finished product thus generally contains an unreasonably high water content (e.g., 85 percent by weight or greater), rendering the product expensive to dry. An additional waste material in the form of the wash water is also created which is difficult to treat due to the presence of the sugars and other peel-derived components which have been extracted from the peel. It is therefore desirable to provide an improved process for the treatment of the waste materials derived from the processing of citrus fruit in order to produce a variety of useful products which are suitable for human and animal consumption. It is also desirable to provide a process which is more attractive economically as well as more efficient than the processes conventionally employed in the citrus fruit processing industry.